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Hamilton’s 30-year career with Fish & Wildlife—one that started when he was a teen with a curiosity about nature sparked by building waterfowl pens and banding ducks and geese—included a stint on the Young Adult Conservation Corps, a dozen years as director of FWS’ Southeast Region, and most recently, six months as one of President Obama’s top nature and environment guys.

Some highlights of his three decades at FWS (from his Department of the Interior bio and testimony before the Senate Environment and Public Works Committee last July) include:

He worked by the philosophy, “As the wildlife goes, so goes the nation,” expressing to the Senate Committee last July his concerns and ideas about how climate change is affecting wildlife and birds.

“We now have incontrovertible evidence that many species of America’s birds are in serious trouble,” he said, referring to the 2009 State of the Birds report, on which the National Audubon Society collaborated. But, he concluded, “bird populations show amazing resilience and ability to recover when the health of their habitat is sustained or restored.”

Hamilton was just 54. He died after suffering from chest pains while skiing, according to the Associated Press.